Acropora Growth

Introduction

When looking at the coral growth patterns of frags you may notice that the base encrusting process stops early and does not pick up later. This seems common with the Acropora I have propagated and a requirement of the coral frag for faster development (branches offer more surface area). However, this makes the coral appear somewhat unnatural, more like a tree than a bush. I would like to see much greater encrusting growth and have given some thought to this.

Growth Rates

I have now experimented with mounting Acropora frags sideways or horizontal rather than vertical. This configuration is after all the way things work in nature. As branches are knocked off and fall to the rocky substrate, they rarely land vertically. Instead they lay horizontally where a maximum amount of tissue can touch the rock. This page documents a differential experiment mounting several frags from the same host Acropora in both planes. The f irst three photographs form a time-lapse of the same green branch Acropora sp. that was looked at in the propagation page. Here the orientation is horizontal. The last two photographs are the same species mounted in the vertical plane.

The first picture was taken right after attaching the cutting sideways to a small piece of live rock. The second picture was taken one month later and shows encrustation along the full length of the base as well as several branches developing. The third picture is the coral after three and a half months more growth. As you can see this species of Acropora is a real grower, especially when frags are mounted horizontal. The picture was taken at 1/2 the magnification of the previous shot. The total grow-out time for this coral frag was 18 weeks, the same as the frag featured in the propagation page for this coral -

Additional Notes 1

The difference in geometry and the fullness of the branching of this frag when compared to the earlier grow-out. The one real difference is that this one was mounted horizontally and the previous one was mounted in the more commonly seen vertical plane. The picture shows a pair of plugs on a single rock. This propagation was done at the same time as the horizontal mount attachment and was an attempt to take a single long branch and make two plugs by cutting it in half. This leaves one of the cuttings with two cut ends and the other with a single cut end. The idea is that the exposed cut end would heal over and the frag would continue to grow as normal. As you can see from the picture, the tops are healed over and some growth has occurred there -

However, you will noticed that these plugs have not grown much at all. Very little encrusting growth and no branching at all. It would appear as though this grow-out attempt is stalled. The reason? Well, if you look very closely at the polyp structure you will noticed that I managed to get both plugs in upside down! Normally, for vertical mount, one puts the plugs in with the polyp structure pointing up. In this case I got it wrong and the structures point down. I can only attribute the delay in growth to this reversal in direction. So, for now anyway, I would recommend that the polyps point up for vertical mounting. If you look very closely at the point just above the middle of each plug (this is where the tissue is new and slightly brownish in color), you will see that the new growth (above this point) has the polyps going in the correct direction. Below this point, the polyps point down. It is almost as if the coral is trying to encrust at what it thinks is the bottom but, because there is no base to encrust to, it simply continues to grow out at the 'top' and very little or no encrusting occurs at the 'bottom'. In other words, the coral growth pattern seems to be polarized along its branch axis and is not symmetrical in its behavior. Well that is of course conjecture, but the growth process is an interesting one. The picture shows the same two plugs three and a half months later. Notice that while the plugs did grow vertically and did finally show some encrusting growth at the base, there are relatively few branches and those that did grow out and short and stubby. Not only is there stunted growth, but the small growth that did occur is deformed, exaggerated in the vertical plan and irregular. In my opinion, this is not the sort of growth pattern one would find in nature and would reject it for my tank. I would much prefer the horizontal mount growth morph. Based on these results I believe I can recommend horizontal mounting of Acropora spp. frags.

By John Rice